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MBT Timing and Engine Life

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Hi Andre I was wondering from all the video I watched from your course about tuning MBT timing , how does it effect a engine life when we tune for MBT timing on Factory stock engine if we are not knock limited and using e85?

Will my engine last a lot longer running 10 degrees less than MBT across the entire power band vs using MBT?

I had this concerned because I noticed Subaru Pump gas tune and E85 tune can have 10 degrees difference, but i wasn't sure running MBT timing will reduce Motor life significantly that i should let customer know and decide how far they want to go if we aren't knock limited.

There are a couple of considerations here:

1. Obviously we need to stay away from knock, and this often results in us not being able to achieve MBT timing on pump gas.

2. The engine will have a mechanical strength limit and exceeding this even once will result in component failure.

3. As well as the ultimate tensile strength of a component, the engine components will also have a fatigue life.

What this all means is that if we exceed the ultimate tensile strength of a conrod even once, it will break. If you run it continuously near to this limit though it will become fatigued over time and may fail. Where these points sit is obviously very dependent on the specific engine so this requires some knowledge and experience with the engine you're tuning. It also depends on the way the engine is going to be used. For example there are plenty of guys in the US who have pushed the stock FRS engine to 700 whp (or thereabouts) on E85 without failure. That's probably ok for a dyno queen but if you wanted to take that same engine and punish it around a race track for 15 laps I'd be taking bets as to how long the poor rods would last.

So the simple answer - It depends. Personally I'd be unconcerned about reducing the life expectancy on a stock turbo configuration. Once you start pushing the torque higher with a bigger turbo though you do need to think about the potential outcome.

On a stock block EVO 9 we tuned to 500 kW atw, we purposely reduced both boost and ignition timing around peak torque to reduce the load on the rods and give the engine the best chance of surviving. Disclaimer: No, I wouldn't recommend running 500 kW atw on a stock block EVO 9 ;)

Got it thanks

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